In an AC unit, it is common to provide a main partition in the unit with the evaporator being on the room side (interior) of the partition and the condenser and compressor being on the outside. During operation, the room air is recirculated through the evaporator for cooling. In a heat pump heating unit, the operation is in reverse, i.e., the room side being the condenser and the outside being the evaporator. In certain operations, it is desirable to introduce fresh air from the outside to mix with the recirculating air. For certain specified applications, it may be necessary to provide fresh air at up to 150 cubic feet per minute (CFM). Existing units generally only provide about 50-70 CFM of fresh air, which may not meet building codes and standards.
In most prior art designs, the evaporator blower wheel brings in the fresh air through one or more openings in the main partition. These openings have been located in areas of convenience and are accordingly only marginally effective at drawing in fresh air. More specifically, in most single-motor AC units, the evaporator motor is typically mounted to the outside of the main partition and its shaft extends through a hole in the partition to the evaporator blower wheel which is enclosed in a scroll. When fresh air is desired, a vent door in the main partition is opened and a path is provided for air to flow by evaporator blower wheel suction. The incoming fresh air mixes with the recirculation air as it enters the front of the evaporator blower wheel through the recirculation air orifice. With such a configuration, the fresh air flow rate is substantially below current new building standards. Further, because the flow of fresh air through the fresh air vent is drawn by a relatively slight negative pressure created at the vent door by the evaporator blower wheel, the flow rate can be substantially influenced by other factors such as the condenser fan or by interior roomside static pressure. More specifically, if the condenser fan on the back side of the partition is on at the same time that the vent door is open, some of the air which would otherwise be drawn through the main partition as fresh air could be drawn by the condenser fan and passed through the condenser to the outside. Examples of prior AC and/or heating units having fresh air ventilation are disclosed in U.S. Pat. Nos. 4,524,588; 4,553,405; and 5,372,189; which are incorporated herein by references.
Therefore, there remains a need to improve the fresh air ventilation capacity of existing AC and/or heating units.